IFN was first discovered as a virus-growth-inhibitory factor produced from virus-infected cells. There have been known that there are three different types of IFN, i.e., IFN-α/β, γ and λ with different receptors and there exist at least 13 different types of human IFN-α subtypes. Human IFN-α in the form of a recombinant preparation produced with E. coli or a natural preparation prepared by stimulating peripheral leukocytes or lymphoblastoid cells, as an established cell line, stimulated with Sendai Virus of Japan (HVJ). Such human IFN-α has been extensively, clinically used as therapeutics for malignant neoplasms such as renal cancer and type B/C hepatitis. IFN has been researched on its immunoregulatory action and its relation with autoimmune diseases such as allergic diseases and diabetics, as well as diseases induced by virus infections, and also it has been concerned on its in vivo dynamics. For assaying IFN activity, bioassay based on its anti-viral activity using culture cells has been used. Such bioassay well reflects the physiological activity of IFN, however, it is known that, for example, it requires considerably longer period of time for assaying and it is susceptible to factors that influence on the physiological functions of the cells used for assaying. When stimulated with viruses, etc., leukocytes and lymphoblastoids produce natural types of IFN including its plural types and subtypes (see, Yanai Y. et al., Journal of Interferon & Cytokine Research, Vol. 21, No. 10, pp. 835-841, 2001). Therefore, direct assay for activity of these subtypes and analysis of their functions were quite difficult.
Plurality of anti-human IFN-α monoclonal antibodies have been prepared to quantify and purify human IFN-α (see, for example, Japanese Patent Kokoku No. 11235/94, Japanese Patent Toku-Hyo 2004-533217, and Japanese Patent Kokai No. 2007-63177). A monoclonal antibody which specifically binds to human IFN-α subtype α4 (“human IFN-α subtype α4” will be abbreviated as “IFNα4”, hereinafter) (see, for example, Molecular Immunology, Vol. 29, No. 3, pp. 391-399, 1992) has been prepared, and a kit for specific quantification of human IFN-α using a mouse monoclonal antibody has been commercialized (see, for example, “Kit for Assaying Human IFN-α”, a product name of and commercialized by JIMORO Co., Ltd., Gunma, Japan), however, it could not specifically recognize IFN-α subtypes.
It is known that IFN-α8 exists in three types of molecules called IFNα8a, IFNα8b, and IFNα8c (see, for example, International Patent Publication No. WO 2006/051805). Since IFNα8 has a superior physiological activity to those of human IFNα subtypes α2a, α2b, etc., as conventional pharmaceutical ingredients, there has been proposed therapeutic medicaments for susceptive diseases, containing IFNα8 or mutant proteins thereof (see, for example, International Patent Publication No. WO 2006/051805 and Japanese Patent Toku-Hyo-Hei 9-509955). Since some of these human IFNα subtypes are pointed out that they possibly function as a co-agonist (an enhancer) for other subtypes (Japanese Patent Toku-Hyo-Hei 9-509955) and there exist IFNα8 mutant proteins with different specific activity (International Patent Publication No. WO 2006/051805), an assay system like bioassay, which specifically, accurately, and highly-sensitively quantifies proteins without being affected by other physiological factors, is required in case of researching physiological functions of human IFNα subtypes and mutant proteins thereof and studying through comparison of their physiological activity and blood dynamics in exploring medical preparations. Although monoclonal antibodies recognize specific epitopes but have different specificity and affinity, any monoclonal antibody suitable for constructing an assay system specific to IFNα8 and having high-sensitivity must be explored. To apply IFNα8 or its mutant proteins for pharmaceutical use, the above-identified IFNα8 and its mutant proteins should be purified specifically and massively, there needed is a monoclonal antibody suitable for preparing an antibody column, which has lesser non-specific adsorption on IFNs other than IFNα8 and its mutant proteins, and which facilitates the elution of IFNα8 and its mutant proteins from a column prepared with the monoclonal antibody.